The present invention relates to nail guns and similar construction, manufacturing or assembly devices, and more particularly relates to an apparatus and method for restricting operation of such devices under certain operational circumstances.
A variety of construction, manufacturing, or assembly tools operate by discharging fastening devices towards a target material. Such tools include, for example, nail guns and staplers. Typically, the fastening devices that are discharged from these tools are projected at high velocities, so that the fastening devices effectively penetrate, and become secured with respect to, the target material.
Often these tools must be used at a rapid pace by construction workers and other operators. To facilitate such rapid use, the tools often include mechanisms that reduce the amount of effort that the operator must put forth in order to cause the tools to discharge the fastening devices. For example, nail guns often include pressure sensing devices near the tips of their barrels so that the nail guns discharge fasteners immediately once the nail guns are pressed onto the target material, without any additional triggering action on the part of the operator.
Due to the rapid pace at which the tools are used, combined with possible fatigue of the operators, or even due to carelessness on the part of the operators, the tools can be misdirected toward the operators themselves or toward other human beings.
To avoid the discharge of fastening devices when the tools are so misdirected, it would be advantageous for the tools to have a feature that allowed the tools to automatically determine whether the tools were being misdirected and, while determining this to be the case, rendered the tools disabled from discharging fastening devices. It would further be advantageous if such a feature in the tools did not significantly restrict the pace at which the tools could be used in construction, manufacturing, or assembly.
The present inventor has realized that a coil can be placed on the tip of a nail gun or similar device and be employed as part of a sensor to determine whether the tip of the nail gun is abutting human flesh as opposed to a standard target material such as wood or metal. The coil forms part of a resonant tank circuit of the sensor, and produces a magnetic field that causes eddy currents to occur within the abutting material in accordance with Lenz""s law. The eddy currents in turn can produce a change in the quality factor of the tank circuit, and the inductive or capacitive nature of the material will cause a change in the resonant frequency of the tank circuit. The sensor is able to determine a resistance of the abutting material based upon the change in the quality factor and a reactance of the abutting material based upon the change in the resonant frequency. By comparing the measured resistance and reactance values with known values associated with different materials, the sensor is able to generate a signal indicating when the abutting material is human flesh or some other non-construction material, such that the nail gun should be disabled and allowed to fire only upon an operation override.
In particular, the present invention relates to a device for discharging fastening elements. The device includes a body having a location at which the fastening elements are discharged, and a sensor circuit supported by the body. The sensor circuit includes a conductive coil proximate the location and further includes a capacitive element, a frequency detector, an oscillator, an amplitude control circuit and a processor. The capacitive element is connected in parallel with the conductive coil so that the capacitive element and the conductive coil form a resonant tank circuit. The frequency detector is connected to the resonant tank circuit, detects a frequency of oscillation of the resonant tank circuit as affected by a material proximate the conductive coil and outputs a frequency signal indicative thereof. The oscillator has an output terminal and a control terminal, where the output terminal is connected to the resonant tank circuit, and where the oscillator drives the resonant tank circuit at the resonant frequency of the resonant tank circuit as affected by the material proximate the conductive coil. The amplitude control circuit is coupled to the oscillator, receives an electrical signal from the output terminal, and in response generates a control signal that is provided to the control terminal of the oscillator. The processor receives the frequency signal and an additional signal that is functionally related to the control signal. The processor provides an output signal that prevents the device from discharging at least one of the fastening elements when the processor determines that the frequency signal and the additional signal indicate that the material proximate the conductive coil is a particular material into which the fasteners should not be discharged.
The present invention additionally relates to a tool for discharging fastening devices. The tool includes means for discharging the fastening devices, and means for determining when the fastening devices are to be discharged, where the determining means is coupled to the discharging means. The tool additionally includes means for generating an oscillatory signal, where a resonant frequency of the oscillatory signal depends both upon characteristics of the generating means and also upon a material proximate at least one portion of the generating means, and where the generating means is supported by the discharging means. The tool further includes means for detecting a frequency of the oscillatory signal and producing a first signal indicative thereof, where the detecting means is electrically coupled to the generating means. The tool additionally includes means for producing a second signal indicative of a quality factor of the oscillatory signal, where the quality factor depends at least in part upon the material proximate the at least one portion of the generating means, and where the producing means is coupled to the generating means. The tool further includes means for providing a third signal to prevent the determining means from causing the discharging means to discharge at least one of the fastening devices, where the third signal is provided in response to the first and second signals.
The present invention additionally relates to a method of preventing a tool from discharging a fastening device into human flesh. The method includes exciting a resonant tank circuit having a coil with an electrical signal to produce an oscillatory signal within the resonant tank circuit and an electromagnetic field that envelops a material that is proximate the coil, where the electrical signal is continually adjusted to be at a resonant frequency of the resonant tank circuit as affected by the material. The method additionally includes generating a frequency signal indicative of a frequency of oscillation of the oscillatory signal, which is the resonant frequency of the resonant tank circuit as affected by the material. The method further includes generating a control signal for controlling an amplitude of the electrical signal so that the oscillatory signal tends toward a constant amplitude. The method additionally includes processing the frequency signal and an additional signal that is functionally related to the control signal to determine whether the material has a resistance and a reactance characteristic of human flesh. The method further includes, when the processing of the frequency signal and the additional signal indicates that the material has the resistance and the reactance characteristic of human flesh, producing an output signal that causes the tool to become disabled from discharging the fastening device.